The present invention relates generally to a steam turbine and more particularly to a dovetail assembly for attaching a steam turbine rotating blade to a steam turbine rotor wheel.
Generally steam turbine rotating blades and steam turbine rotor wheels in the latter stages of a low pressure turbine are usually highly stressed during operation due to large centrifugal loads applied by the rotation of longer and heavier latter stage blades. In particular, large centrifugal loads are placed on the blades due to the high rotational speed of the rotor wheels which in turn stress the blades. These loads induce higher average and local stresses in the connective dovetails that attach the blades to the rotor wheels. These stresses along with moisture from the steam flow path of the steam turbine drive stress corrosion cracking. Both the higher average and local stresses concentrations can lead to lower fatigue life and stress corrosion of turbine rotor wheels and blade dovetails. Reducing stress concentrations and stress corrosion cracking in the dovetails under large centrifugal loads is a design challenge for steam turbine manufacturers, especially as the demand for longer blades increases.